The present invention relates generally to air-fuel controls for engines and, more particularly, to an air-fuel control for open loop operation of an internal combustion engine. The control has two stages of operation: the open loop (first stage) operation is based on calibrated adjustments derived from momentary closed loop (second stage) operation.
Most internal combustion engines have an air-fuel distribution control that regulates the air-fuel mixture provided to the engine during operation. The engine also has an exhaust system that includes an exhaust conduit to carry exhaust gas away from the engine as well as an exhaust gas oxygen ("EGO" or "ego") sensor. The EGO sensor detects the level of oxygen in the exhaust gas and provides a signal to the air-fuel distribution control to increase or decrease the amount of oxygen in the air-fuel mixture being supplied to the engine. The EGO sensor often operates much as a switch, giving a high (or "one") value when the air-fuel ratio is below a predetermined level and a low (or "zero") value when the air-fuel ratio is above the predetermined level.
A feedback mechanism, however, that simply advises the air-fuel distribution control as to whether or not the oxygen concentration in the exhaust gas is above or below a predetermined set point does not allow for optimum performance in every engine, since engines and their operating environments vary. The air-fuel mixture supplied to an engine often needs to be adjusted upward or downward, depending on a variety of different variables.
Prior art references disclose the use of oxygen sensors. For example, U.S. Pat. No. 4,953,351, issued to Motz et al., discloses a combustion control. The Motz et al. patent states that control operation for an engine may be impaired by several factors (such as the aging of the lambda probe). In order to allow for such factors, the set point of the controller is adjusted under certain conditions or at certain intervals. Thus, information as to whether or not the exhaust gas oxygen level concentration is above or below a predetermined set point of a particular oxygen level sensor does not, by itself, necessarily ensure that all engines under all conditions will operate at an optimum air-fuel ratio.
Variations in engine fuel control, variations in engine tolerances, the type of exhaust system used with the engine, the acceleration and deceleration inputs provided to the engine by the driver of the vehicle, the quality of the combustion occurring within the engine, the speed and load experienced by the engine, the altitude of the vehicle above sea level, and the temperature of the vehicle, and as well as other environmental factors and the age of the lambda probe, all influence the air-fuel ratio that is optimum for a particular engine. Unfortunately, many of the presently available air-fuel controls do not allow for a correction of the air-fuel injection system, so as to determine the effect of all the above conditions on the optimum air-fuel ratio.